Position sensing is used to electronically monitor the position or movement of a mechanical component. The position sensor is coupled to an actuator and is adapted to produce an electrical signal that varies as the position of the component in question varies. Actuator and sensor assemblies are included in many products. For example, actuator and sensor assemblies allow the status of various automotive components to be monitored and controlled electronically.
A position sensor needs to be accurate, in that it must give an appropriate electrical signal based upon the position measured. If inaccurate, a position sensor may hinder the proper evaluation and control of the position of the component being monitored.
Typically, it is also a requirement that a position sensor be adequately precise in its measurement. However, the precision needed in measuring a position will obviously vary depending upon the particular circumstances of use. For some purposes, only a rough indication of position is necessary; for instance, an indication of whether a valve is mostly open or mostly closed. In other applications, more precise indication of position may be needed.
A position sensor should also be sufficiently durable for the environment in which it is placed. For example, a position sensor used on an automotive valve may experience almost constant movement while the automobile is in operation. Such a position sensor should be constructed of mechanical and electrical components adequate to allow the sensor to remain sufficiently accurate and precise during its projected lifetime, despite considerable mechanical vibrations and thermal extremes and gradients.
In the past, position sensors were typically of the “contact” variety. A contacting position sensor requires physical contact to produce the electrical signal. Contacting position sensors typically consist of potentiometers that produce electrical signals which vary as a function of the component's position. Contacting position sensors are generally accurate and precise. Unfortunately, the wear due to contact during movement has limited their durability. Also, the friction resulting from the contact can degrade the operation of the component. Further, water intrusion into a potentiometric sensor can disable the sensor.
One advancement in sensor technology has been the development of non-contacting position sensors. A non-contacting position sensor (“NPS”) does not require physical contact between the signal generator and the sensing element. Instead, an NPS utilizes one or more magnets to generate magnetic fields that vary as a function of position, and devices to detect varying magnetic fields to measure the position of the component to be monitored. Often, a Hall Effect device is used to produce an electrical signal that is dependent upon the magnitude, polarity, or direction of the magnetic flux incident upon the device. The Hall Effect device may be physically attached to the component to be monitored and thus moves relative to the stationary magnet(s) as the component moves. Conversely, the Hall Effect device may be stationary with the magnet(s) affixed directly or indirectly to the component to be monitored. In either case, the position of the component to be monitored can be determined by the electrical signal produced by the Hall Effect device.
Although currently available actuator and NPS assemblies have proven satisfactory, there continues to be a need for improved, lower cost actuator and NPS assemblies.